3-KIDD presentation BIOL350

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Stable Nitrogen Isotope Ratios and Organochlorines in Biota from a Freshwater Food Web

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Things to focus on for presentation (Delete After)

Defining Important Terms and Concepts

Introduction

Methods

The samples collected for this experiment were both fish and invertebrates – the invertebrates were mostly collected from the guts of the fish. The samples were frozen after all water was depleted to eliminate any weight water weight by drying them in an oven for 1 week at 60 degrees celcius.

Essentially there were 2 methods used in this experiment;

The first method used was the Stable Isotope Analysis. This method is used to determine the distribution of stable isotopes within a chemical compound in an organism. For this experiment, 15mg of dried tissue was vacuum-sealed in a Vycor tube (highly thermal resistant tube) with 1g copper wire, 1g copper oxide wire, and 1mm2 piece of silver foil. The tissue in the tube was then combusted at 850oC for 4 hours and 600oC for 2 hours. After combustion, the isotope ratios were analyzed by a dual inlet isotope ratio mass spectrometer to determine isotope distribution.

The second method used was the organochlorine analysis. This method is used to determine the concentration of organochlorine molcules within an organism – often from pesticides. In this experiment 5-20g of liver and muscle tissue were mixed with dry ice and then anhydrous sodium sulfate. Then to calculate extraction efficiencies, aldrin and octachlornapthalene was added. Liver tissues were mixed with hexane and centrifuged for 30 minutes, while the muscle tissues were extracted using hexane. Then using a gel chromatography, the chlorinated hydrocarbons were eluted from the muscle and liver tissues and the concentration could therefore be calculated.

Results

From the Stable Isotope Analysis, it was determined that there were lower concentrations of N15 in the lower trophic levels then the higher trophic levels. An average increase of 5.2% of N15 occurred between the prey and its predator. There were very similar trends in the concentrations of DDT (dichlorodiphenyltrichloroethane), HCH (hexachlorocyclohexane) and HCB. Since there were very similar trends, a t-test was calculated to determine whether the N15 percentage in a trophic system is related to the concentration of DDT, HCH, and CHB. DDT and CHB had a stronger correlation with the percentage of N15 isotope then HCH meaning DDT and CHB increased more proportionally to the increase in N15 isotope.

II. A Critical Analysis of the Study Design

Deviations from Expected (?) by  15 N

Expected:

3-5 permil increases with each trophic level

range of 2.0 permil within each trophic level

Broad whitefish were observed to have lower than expected delta-15N difference from invertebrates

1.8 permil increase observed

Explained by migratory behaviours that likely include a diet shift

Large range, 4.0 permil, observed in lake whitefish

May be due to occasional piscivory

Predatory invertebrates may also be adding an unexpected trophic level

Biomagnification of Organochlorines

Both wet weight and lipid weight of all three contaminants increased with trophic level

Summary of Important Results (Be selective, won’t have time to present ALL the results): What are the relevant, big-picture results and conclusions? (Contextualize findings for audience) – Phil

Discussion: Discuss the relevance and importance of the conclusions to ecology, ‘P2:Critical analysis of study design*’, discuss results and conclusions (strengths/limitations of their study, Do their conclusions/interpretations match what their results really show? Have they adequately answered the research questions posed?)

Toxic equivalents of PCDD/PCDF increased in concentration with trophic levels

This study examines relationship between 15N and contaminants in biota from a subarctic freshwater lake, Lake Laberge

Trout have higher DDT concentration in this lake than Great Lakes

Source of HCH,DDT,CHB is believed to be atmospheric transport and deposition is found to be in Canadian Arctic

Phil

Phil

Jessie

Discussion of Results

Results and conclusions

Do their conclusions/interpretations match what their results really show?

Jessie

Discussion of Results

Jessie

Discussion of Results

Jessie

Discussion of Results

Manni

Have they adequately answered the research questions posed?

1) HCH, a less lipophilic contaminant was found to have lower slopes than DDT and CHB which relates to the biomagnification potential of lipophilic contaminants.

In other words, the more lipophilic a contaminant is the greater the biomagnification potential (Why are lipophilic contaminants a concern? The biology of relevant organisms, aquatic, terrestrial, vs. mammals whereby aquatic organisms bind lipophilic substances)

In aqueous systems, organisms are exposed to contaminants via multiple routes (Fig. 9.1). The extent of contaminant accumulation ultimately depends on the extent and mode of interaction with diverse contaminated media. The influence of lipids on contaminant uptake likewise varies according to the route by which the exposure takes place and the lipophilic character of the contaminant. Thus, it is necessary to clarify the environmental sources of contaminants for accumulation. The means by which contaminants, once accumulated, can be eliminated from an organism can also depend on organism lipid content. This elimination can be modified by the route, contaminant lipophilicity, and extent of contamination of the environmental compartment into which elimination occurs (http://link.springer.com/chapter/10.1007/978-1-4612-0547-0_10)

In other words, the accumulation of lipophilic compounds in these organisms

2) The goal of this study was to develop a predictive relationship between the lipophilic nature of a compound and its increase in concentration through the food web and to some extent this was achieved. However, additional analysis of slopes is needed “

Strengths/limitations of their study

Limitation: One limitation is that the results have been gathered from one study site over a short study period (XXXX-YYYY). For more confidence in results and any social impact they hope to achieve using these results, more data will be necessary, but this is the case with all scientific studies

Limitation: Relies of heavily on analysis of slope without proving that there is an actual predictive relationship, very strongly suggested

Causation vs. correlation: Does the increase in concentration through the food web alter the compound to increase lipophilic nature (Positive feedback system) OR is it the lipophilic nature of a compound that increases concentration found in food web

“The higher concentrations of organochlorines and higher percent lipid in burbot liver when compared to other fish muscle may have increased the slopes of the regressions between 6aSN and wet weight contaminant concentrations, as was found in regressions of 615N versus lipid. For this reason, whole body concentrations of organochlorines would be a better indicator of biomagnification because they would remove interspecies variation in tissue concentrations of organochlorines.” pp. 8

% lipid in biota from Lake Laberge was significantly correlated with 15N levels., relationship between 15N and organochlorines STRONGER (ie. much more significantly correlated)

HCH concentration did not magnify as much as the more lipophilic compounds DDT and CBH

biomagnification potential may be represented by degree of slope of regression

15N can be used for further studies of the biomagnification of lipophilic organochlorine through aquatic food webs

Relevance and its importance of conclusions to ecology

In a broader sense, Chemicals are a vital part of everyday life. They come in the form of fuels, antibiotics, pesticides, plastic containers, agricultural fertilizers, photocopying compounds, and so on. Society cannot survive in its present form without them. Growth in the numbers of chemicals used during recent decades has been extraordinary (http://link.springer.com/chapter/10.1007/978-1-4612-3810-2_3)

Significant because they were able to correlate 15N to various contaminants and thus, movement of those contaminants up trophic levels

Their results revealed and enforced notion that physiological factors need to be considered when interpreting an organism’s trophic position from 15N

For example, winter months, when they do not food, tissue heavier in 15N

Seasonal shifts that affect interpretation of 15N

Possibility of intraspecies variability (ie. Movement of contaminant up food web is not primarily due to lipophilic nature, may be compounded and synergistic in its manner if poor nutritional status! More likely to take up contaminant because it is hungry not because contaminant is lipophillic) due to factors other than trophic position such as nutritional status

Slopes of regressions of 15N vs. organochlorines indicated that HCH did not biomagnify to same extent as MORE LIPOPHILLIC compounds (DDT, CHB). So, biomagnification potential of a compound may be represented by degree of slop of the regression

Using 15N as a measure of trophic position significant to future studies of biomagnification of lipophilic organochlorines through aquatic food webs

“The higher concentrations of organochlorines and higher percent lipid in burbot liver when compared to other fish muscle may have increased the slopes of the regressions between 6aSN and wet weight contaminant concentrations, as was found in regressions of 615N versus lipid. For this reason, whole body concentrations of organochlorines would be a better indicator of biomagnification because they would remove interspecies variation in tissue concentrations of organochlorines.” pp. 8

% lipid in biota from Lake Laberge was significantly correlated with 15N levels., relationship between 15N and organochlorines STRONGER (ie. much more significantly correlated)

HCH concentration did not magnify as much as the more lipophilic compounds DDT and CBH

biomagnification potential may be represented by degree of slope of regression

15N can be used for further studies of the biomagnification of lipophilic organochlorine through aquatic food webs

Relevance and its importance of conclusions to ecology

In a broader sense, Chemicals are a vital part of everyday life. They come in the form of fuels, antibiotics, pesticides, plastic containers, agricultural fertilizers, photocopying compounds, and so on. Society cannot survive in its present form without them. Growth in the numbers of chemicals used during recent decades has been extraordinary (http://link.springer.com/chapter/10.1007/978-1-4612-3810-2_3)

Significant because they were able to correlate 15N to various contaminants and thus, movement of those contaminants up trophic levels

Their results revealed and enforced notion that physiological factors need to be considered when interpreting an organism’s trophic position from 15N

For example, winter months, when they do not food, tissue heavier in 15N

Seasonal shifts that affect interpretation of 15N

Possibility of intraspecies variability (ie. Movement of contaminant up food web is not primarily due to lipophilic nature, may be compounded and synergistic in its manner if poor nutritional status! More likely to take up contaminant because it is hungry not